MILAN - A study published in the journal Environmental Research Letters has shown that humans are responsible for climate change. The document was compiled by 40 eminent academics, who analysed tree rings, used climate models and historical data taken by the documentation produced by doctors, priests and monks in ancient times. Since 1986, the research concludes, summer temperatures have been around 1.3 °C higher compared to two millennia ago, heat waves have lasted longer and have become more frequent and persistent.

Research coming from afar

"This level of warming does not have precedents in the last two thousand yearssaid Prof. Jürg Luterbacher, coordinator of the report. It is exceptionally high and cannot be explained by natural variability phenomena, tropical volcanoes or solar transformations". Most part of the data relative to the period prior to 755 has been obtained from the analysis of tree rings of pine trees in Finland, Austria and Sweden. These plants, indeed, grow during the hot season, and stop growing with the cold. Their rings and density changes partially correlate with summer temperatures. "The recent heat anomaly is particularly evident in Southern Europe, where variability is generally smaller, and where it is expected that traces of anthropogenic climate change will emerge first", wrote the experts in the document.

Progressive temperature increase

According to the results, temperature fluctuations in the past were greater than what thought until now. In particular, summers have been hotter between the Roman time and the III century, before a general cooling took place until the VII century. A hot medieval interlude was then interrupted by the "small glacial age", well loved by climate change deniers, which lasted from the XIV to the XIX century. Conversely, since when dawn rose on the XX century, the effects of climate change have become progressively more pronounced.

by Alessandro Michielli